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Improving the Plan Quality and Treatment Efficiency Via Flattening Filter Free (FFF) Beams for Single-Isocenter/multiple-Lesions VMAT Lung SBRT

L Sanford*, J Molloy , M Bernard , M Randall , R McGarry , D Pokhrel , University of Kentucky, Lexington, KY


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Patients with multiple lung lesions may not tolerate long treatment times associated with SBRT using traditional treatment planning with individual isocenter per lesion. Treating multiple lesions synchronously with a single-isocenter VMAT plan utilizing FFF beam potentially resolves this issue and improves patient comfort. Herein, we quantitatively compare dosimetry and treatment delivery efficiency of FFF vs with flattening filter (FF) beams in treatment of single-isocenter/multiple-lesions VMAT lung SBRT.

Methods: Fourteen patients with early-stage non-small-cell lung cancer lesions (two to five) received single-isocenter non-coplanar VMAT SBRT. Patients were treated with 6X-FFF and Acuros-based dose with single-isocenter placed between/among lesions. Average isocenter to tumors distance was 5.6cm. Mean tumor volume derived from 4D-CT scans was 38.7±22.7cc. Prescriptions were 54Gy/50Gy in 3/5 fractions (70-80% isodose line). For comparison, these plans were re-optimized with 6X-FF and 10X-FFF beams. Original clinical and re-optimized plans were compared according to RTOG-0915 compliance, target conformity, heterogeneity and gradient index and dose to organs-at-risk (OAR). Additionally, modulation factors and beam-on times were evaluated.

Results: All plans were acceptable for target coverage and OAR doses. 6X-FFF provided better target coverage and statistically significant OAR sparing compared to 6X-FF and 10X-FFF plans. Although, skin sparing was slightly better with 10X-FFF by about 1.0Gy, on average. Furthermore, 6X-FFF showed less beam modulation, which is desirable for lung SBRT. Average overall reduction of beam-on time of 75% and 60% was found when using 10X-FFF (2.3min) and 6X-FFF (3.4min), respectively, compared to 6X-FF beam (8.6min).

Conclusion: Superior plan quality and faster treatment delivery compared to 6X-FF is achieved with 6X-FFF for single-isocenter/multiple-lesions lung SBRT–perhaps quicker throughput of patients, improving clinic efficiency. Utilizing 10X-FFF will result in even faster treatment with greater skin sparing (for selected patients) with slightly higher dose to OAR’s but could potentially reduce intrafraction motion error and further improve patient compliance.


Flattening Filters, Treatment Techniques, Treatment Planning


TH- External beam- photons: extracranial stereotactic/SBRT

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